It should be possible to supply a Reporter that emits legacy messages, as mentioned in the previous comment. That should be a design goal.
Another easy goal is to support filtering of messages, as also mentioned previously.
Another possible goal is support of downstream linters. I’d like my pluggable linter to work with my pluggable message suppression system and other reporting components so that clippy can offer advice about lints.
An example wart in the current API is the “re-run with different options for more information” message, which has to be customized for different tool environments. It’s easy to slip into vendor lock-in.